1. Field of the Invention
The present invention relates to a process and apparatus for loosening or removing the skins from products such as nut kernels, beans, seeds or the like.
2. Related Art
Various devices employing different techniques are known for removing the skins from such products.
With particular reference to nut kernels, devices are known which scrub, brush or scrape the nut kernels, or use other abrasive type treatments to remove the nut kernel skins. In certain cases, 40% of the treated products still have their skins adhered thereto. It is then necessary electro-optically or manually to sort the products and re-treat those on which the skins remain.
In most cases, prior to employing the above skin as removing processes, the nuts are pre-treated to loosen the skins for their more efficient removal. Typically pre-treatment involves soaking the nut kernels in water or a suitable aqueous solution. Alternatively the pretreatment may take the form of roasting the kernels or heating them in hot air, steam, water or an aqueous solution.
The speed and efficiency at which nuts can be processed in these known methods of skinning is reduced by the additional pre-treatment process steps involved. Although necessary in order to attain skinned nuts of the required quality, these pre-treatment steps may thus be undesirable since they add time to the skinning operation as a whole. The apparatus required for such pre-treatments moreover usually involve considerable extra plant investment costs and maintenance costs
Particular forms of pre-treatment also have their particular associated problems. For example, with treatments that involve a nut kernel being heated, the heat so applied can cause damage to the kernel's cell structure, reducing its shelf life and affecting its flavour characteristics. Also, when heating the nut kernel has only been partially successful in loosening the kernel skin, reheating is not desirable due to the likelihood of damage.
Soaking forms of pre-treatment have the disadvantage that they are typically highly time consuming. In one known process for example, nut kernels are soaked in water or sodium hydroxide for about eight hours. Since all the nut kernels have to pass through the soaking step before they are skinned, the output of the skinning process will depend on the amount of nuts which can be soaked at any given time. Soaking in chemical solutions requires careful monitoring in order to ensure that the nut kernels are themselves not damaged by the action of the solution.
It has been proposed in U.S. Pat. No. 4,537,122 to skin almond nuts by fluidising a bed of nuts with air. In this system, the nuts are first presoaked and washed to remove 90-95% of their skins and the remaining 5-10% is removed by the fluidising air. Thus several steps are involved.
It has been proposed in U.S. Pat. No. 4,300,447 to skin peanuts by the abrasive action of a rotating cylinder in combination with jets of air. Again, in this proposal, it is preferred for the raw peanuts to be preconditioned by warm or hot air or hot water or aqueous solution. A significant proportion of the nuts may remain unskinned without such pre-treatment.
It has been proposed in U.S. Pat. No. 2,651,345 to provide a machine which uses water jets as part of a process to remove the skins from hazelnuts. The nuts are contained in a series of parallel elongate chambers where they are supported on rotating rolls having spiral ridges for conveying the nuts along the chambers whilst being subjected to jets of water discharged from fixed nozzles. The rolls form a moving floor of each chamber and the jets are angled to strike the nuts with "glancing blows" when the nuts are positioned centrally at the lowermost region of the chamber, between the rolls. In order to be sure that there are no nuts above a correctly positioned nut, which would shield that nut from the jets, each nut must effectively be conveyed individually along a chamber during the skinning process and this is inefficient in terms of production rates. The machine is complicated in that the rotating rolls have to be provided and in that the jets of water have to be carefully aimed to provide the desired glancing blows. In addition, the rotation of the nuts on the rolls demands, in the main, uniformly spherical and uniformly sized nuts, thereby limiting the types and varieties which can be used in the machine. For example, certain types of hazelnut are "acorn" or "cone" shaped and will not readily turn on the rolls.
A similar rotating roll conveyance system for nuts has been proposed in U.S. Pat. No. 3,077,217. Thus, in this proposal there are also fixed nozzles directing a spray into an elongate chamber having a floor formed by a pair of adjacent rotating rolls, the nuts being conveyed substantially individually along the chamber by a helical groove on one of the rolls. The other roll has an abrasive surface for removing the nut skins, assisted by a hot water spray (140.degree. F. to 175.degree. F.) at a pressure of 40 psi to 80 psi. Because of the need to abrade the nuts at the floor of the chamber, the nuts have to be conveyed individually along the chamber and there are again limitations in production rates and the ability to deal with products of different shape and size.
It has been proposed in U.S. Pat. No. 4,738,860 to provide a machine concerned exclusively with walnuts. The walnuts are subjected to water jets, at a preferred pressure ranging from 30 psi to 100 psi, but this does not itself remove the skins. During spraying the walnuts are contained in cup shaped containment areas formed by a fine mesh fabric net or screen. Although the document suggests that the walnuts can move freely within the containment area during spraying, there will be a tendency, if more than one layer of walnuts are put in the containment area, for there to be a "dead" region at the bottom of the cup-shape where walnuts will remain and thus not be exposed directly to the spray. It will therefore be generally necessary to load the containment area with only one layer of walnuts and this will again impose a limitation on production rates.
Further concerning U.S. Pat. No. 4,738,860, following the application of water jets, the skinned walnuts and the skins are taken together to a centrifuge and thereafter the skins and the nut meat are separated by means of an air blower. The process therefore requires an additional step to remove the skins from the skinned nuts.